1. Field of the Invention
The present invention relates to a method for manufacturing semiconductor light-emitting device, especially to a method for manufacturing semiconductor light-emitting device with high efficiency.
2. Description of the Related Art
Semiconductor light-emitting devices such as light-emitting diodes (LEDs) have high light emission, fast response speed and longer life than other conventional light source. Therefore, the LEDs are promising in lighting application, especially after the successful development of the high-brightness blue LED.
To enhance light-emitting efficiency, the LED can adopt a hetero-junction structure to improve the internal quantum efficiency thereof. However, the light emitted from an active layer of the LED is subjected to total internal reflection (TIR) between the active layer and an upper cladding layer, and between the upper cladding layer and an air interface due to refractive index mismatch. In particular, when the light passes from a medium with a higher refractive index to another medium with a lower refractive index as the light is emitted out, the TIR problem is inevitable, thus degrading the external quantum efficiency of the LED.
FIG. 1 illustrates a schematic, cross-sectional view of a homo-junction GaN-based LED 3. The LED 3 comprises a sapphire substrate 300, a buffer layer 302 on the sapphire substrate 300, an n-type GaN layer 304 and a p-type GaN layer 306, all successively formed on the buffer layer 302. The LED 3 further comprises p-electrode 310 and n-electrode 308 for applying electric power thereto. After applying electric power to the LED 3, light is emitted from an active layer (not label, shown as shaded layer). Part of the light (such as ray R2) suffers TIR in the interface between the p-type GaN layer 306 and air and is reflected into the LED 3, thus degrading the external quantum efficiency of the LED. This problem is irrelevant to the structure of active layer. Therefore, an LED with a hetero-junction structure, single quantum well (SQW) structure or multiple quantum well (MQW) structure also suffers this problem.